1. Field of the Invention
The present invention relates to a handheld working tool according to the preamble of patent claim 1, as well as to a device for vibration isolation of a handle of a working tool.
2. Description of the Related Art
Handheld working tools, in particular drilling and/or impact hammers (hereinafter referred to as ‘hammers’), stampers, or the like, often have a vibration-generating device for producing a vibration that is required to achieve the desired working effect. In drilling and/or impact hammers, this is standardly a hammer mechanism with which an impact against a tool is achieved. However, the strong vibrations should affect the operator holding the tool in his/her hands as little as possible.
Working tools also standardly have a device by which vibrations, shocks, or impacts can be produced. Such devices are hereinafter designated in common as ‘vibration exciters.’
Many such working tools are hand-operated, so that corresponding handles are provided by which an operator can grasp and hold the tool. The vibrations or shocks produced in the vibration exciter of the tool so that it can perform its function are transmitted to the operator via the handles, which is not only unpleasant but is also damaging to health in the long term. An effort is therefore to be made to keep the vibration in the handle as low as possible.
For this purpose, it is known to provide a vibration decoupling device between the handle and the vibration exciter. Standardly, such a vibration decoupling device is realized with the aid of passive spring damper elements. For example, rubber elements can be placed between the handle and the vibration exciter in order to achieve a certain degree of vibration decoupling. Due to the limited constructive space, the spring elements can have only small spring travel, which limits their suitability for vibration isolation of the handle. On the other hand, the spring elements must not be made too soft, in order to enable the operator to precisely guide the work tool.
Hammers are known that have anti-vibration systems with passive spring elements, in particular rubber bumpers. In order to achieve good vibration isolation under various conditions of use, in principle low spring rigidities and large spring travel are to be sought, which however are disadvantageous for the constructive size and handling of the work tool.
In particular, it must be taken into account that, for example in hammers, strongly alternating pressure forces must be dealt with. These result on the one hand from different reaction forces or recoil forces due to different tool types or non-homogenous materials that are to be processed. On the other hand, the pressure forces change due to differently acting weight forces caused by the direction of work (downward, horizontal, upward) as well as different tool weights.
It is often problematic to develop suitable spring elements that take into account all conceivable operating states, in particular the entire possible spectrum of pressure forces.
In DE 196 46 622 A1, a working tool that can be guided using a handle is described. The handle is actively vibration-damped by an actively controlled or regulated compensating element that produces a compensating force or movement dependent on the vibration transmitted to it and originating in the working tool. Through this compensation effect, it is possible largely to equalize the vibration originating in the working tool, so that the handle, connected after the compensating element, is essentially free of vibration. However, the construction expenses and control technology expenses for such a tool are significant.
DE 101 00 378 A1 describes a hand tool machine having a vibration exciter and a vibration isolation device situated between the vibration exciter and a handle. The vibration isolation device has an actuator via which the operating force can be compensated at least partly with an actuating force. Here the actuating force is largely independent of the actually existing vibration that is to be isolated. The vibration itself is compensated by a spring element, situated parallel to the actuator, that has a relatively soft characteristic. In the described working tool, the actuator itself thus does not carry out any vibration-damping function. Rather, it ensures that the working position of the spring element, i.e., its initial tension, is always within a predetermined range, so that the spring element can compensate the occurrent vibration. The actuating force of the actuator is automatically set dependent on the operating force acting from outside, in particular the pressure force of the operator. To this extent, it is possible to speak of a “semi-active” vibration isolation. The actuator can be realized electrically, electromagnetically, or hydraulically, requiring a significant constructive expense.
From DE 101 58 266 A1, a device is known for vibration damping of a handle of a machine tool, in which the handle is connected to the housing of the machine tool via at least one spring. With the aid of an actuator that acts on the spring, it is possible to keep the distance between the handle and the housing of the machine tool almost constant, independent of the actuating force exerted on the handle. The actuator has a ram that can be displaced by means of an electromagnetic, hydraulic, or pneumatic drive.
In EP 0 206 981 A2, a hand tool is described having a drive device that produces vibrations. On a housing that accommodates the drive device, a handle is provided that can be moved parallel to the main axis of vibration, limited between two stops. The handle stop situated in the direction of advance of the hand tool is fashioned as an electromagnet that exerts a constant, controllable force both on the handle and also on the housing, independent of the position of the handle relative to the housing. This is intended to achieve a vibration isolation.